This invention relates to a novel molding apparatus and method and more particularly relates to a new multiaxis rotational molding apparatus and method.
Throughout history, one of the most important activities in most civilizations has been the construction of buildings for various purposes such as dwellings, storage and the like. With primitive societies, it was common to construct such buildings from natural materials that were readily available. In forested areas, structures were erected with logs or boards that had been cut from the logs.
Where trees were less available, people used stone for building materials or more commonly artificial adobe substitutes formed from mud baked in the sun. To make artificial stones or bricks more durable and less likely to crumble, it was customary to mix straw or similar materials with the mud. These are believed to be the first reinforced products.
As civilizations developed, the use of reinforced products has become much more widespread. For example, concrete is formed from mixtures of cement and aggregates such as sand, crushed stone, rocks, etc. In addition, for greater strength metal rods, mesh fabric and the like may be incorporated therein. Wood products of this type include plywood and similar laminated units as well as particle board, wafer board and the like.
With the discovery of man-made polymers and resinous materials, the use of fillers and reinforcing materials therein has become common. These materials may be in a variety of forms including particles, fibers, rods, fabrics and the like.
One of the major problems is the proper incorporation of the reinforcing and/or filler materials into the continuous phase or matrix. Unless a high degree of care is exercised when the materials are combined with the principal component, they may be distributed non-uniformly and/or voids, bubbles and other weak spots may be created.
Even with fillers and reinforcing materials which can be properly placed within a matrix easily, there still is the problem of achieving uniformity of the composition of the matrix. For example, concrete mixes which include cement, water and an aggregate can become non-homogeneous simply by settling on standing. As a result, the trucks which deliver such mixes include drums that are rotated continuously in an attempt to maintain uniformity.
This problem of non-uniformity is significant in most batch processes. Although the obvious solution to the shortcomings of batch processes is continuous processing, most products still are produced on a batch or unit basis even though it might be a continuous batch process, that is, individual units or batches fabricated on an assembly line. As a result, reproducable high quality remains a serious problem.
The production of man-made plastics and resins is an industry that utilizes a high degree of automatically controlled continuous processing. However, for units of appreciable size, batch processing still is the rule rather than the exception. For example, in the production of fiberglass structures such as boats, it is customary to construct the hulls by hand, building on an open mold in which a plurality of resin and fiberglass layers are sequentially laminated or a plurality of mixed resin/chopped fiber coatings are applied over the mold.
Such hand building procedures require a large amount of labor, supervision and continuous inspection to insure that a reasonable level of quality is achieved. This greatly increases the cost of the product.
The problems of batch processing become more complicated when the resins or polymers are foam-forming. As a multi-component mixture is placed into an open mold, the first part of the mixture begins to foam and grow from the bottom of the mold as a result of an exothermic chemical reaction. The bubble size of the foam is smallest at the bottom where the reaction begins and is largest at the top of the mold as the reaction draws to completion. The resulting product is nonuniform in density from top to bottom and thus has poor structural strength and is unsatisfactory.
In view of the above discussion, it is clear that present molding apparatus, methods and procedures do not provide the operating efficiencies and design possibilities required currently and in the future. Thus, there is a need for new molding apparatus and procedures that facilitate the production of products having a high degree of quality and uniformity.